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Squaring up trailers.

Portable Welder

Cast Iron
Joined
Jan 9, 2015
Location
Milan, MI
I have a local trailer dealership that sells around 5,000 trailers a year, they are constantly wanting to bring me trailers that have dog tracking issues, they have other welders that do the easy fixes but like giving me the heavier repairs since I have cranes and beams cast into the floor for doing heavy straightening.
So the first thing I do is to see if the bed is square, if its not I find the center of the trailer at the front and back, I then set my laser at the back and shoot a line up to the center mark at the front of the trailer to see if the coupler is center, if its not, I re-center it.
Once I know my coupler is center, I then measure from the center of the coupler back to the spring hangers diagonally and make sure I have the same number on both sides.
I also use a triangulated method to determine square provided both side rails are parallel.
So my question is, what is an acceptable amount that the coupler can be off center of the trailer, usually if its within about a 1/4" - 5/16" I call it close enough depending on the length of the trailer, the longer the trailer, the more I like to be within 1/8" of an inch.
When measuring from center of the coupler back to the spring hanger diagonally, I dont like seeing it out more than about 3/16".
So I'm trying to walk the line between the customer is being to picky and it's within an acceptable tolerance and NO..., the factory screwed up and the customer should be taken care of.
 
Well, on ones brought to you to fix, how much out is the coupler, and what amount of dogtracking does it produce ?
Might make up a chart.
 
The trailer should be able to handle a greater error as it gets longer. 1/4” is 2.5% error on a 10 foot trailer and half that for a 20 footer.

I like DDoug’ suggestion of recording the errors you’re being asked to fix. I’d imagine some arbitrary fraction of the smallest error that causes a trailer to be returned would do the job. I’d probably shoot for a fifth of that, but I imagine that’s a lot bigger than your current tolerances.
 
The trailer should be able to handle a greater error as it gets longer. 1/4” is 2.5% error on a 10 foot trailer and half that for a 20 footer.

I like DDoug’ suggestion of recording the errors you’re being asked to fix. I’d imagine some arbitrary fraction of the smallest error that causes a trailer to be returned would do the job. I’d probably shoot for a fifth of that, but I imagine that’s a lot bigger than your current tolerances.

The trailer should be able to handle a greater error as it gets longer. 1/4” is 2.5% error on a 10 foot trailer and half that for a 20 footer.

I like DDoug’ suggestion of recording the errors you’re being asked to fix. I’d imagine some arbitrary fraction of the smallest error that causes a trailer to be returned would do the job. I’d probably shoot for a fifth of that, but I imagine that’s a lot bigger than your current tolerances.
I disagree, the longer the trailer, the more noticeable it is.
Years ago at about the age of 23 I welded the tongue on a house trailer that had a rotted tongue that was stored under the trailer, I showed up to weld it on and had to add material to it not understanding the importance of it being centered, the ass of the trailer was hanging half way into the other lane, if the trailer was cut off behind the last axle it wouldn't have hung out into the other lane, but having 20' hanging past the last axle compounded the problem.
30' behind the last axle would have taken the whole lane..., keep in mind, this was 30 plus years ago, so 20' behind the last axle was an example.
 
Yes, if two trailers are off by the same angle, the longer one will stick out further. But the original example wasn’t an angular measurement, it was linear. A 1/4” isn’t an angle and the resulting angle from that 1/4” error will be greater with a shorter trailer.
 
My original post said its more noticeable with a longer trailer...
Nothing here to argue about.

My question was more about what is acceptable tolerance of the customer being to picky.
I feel like I need to be the mediator between the factory and the customer..., whats an acceptable tolerance !!!
 
There is no answer.

Why don't you get down to the root causes? I presume the manufacturer builds the frames on a jig. He's welding the spring hangers at different spots on each frame rail. Fix that issue.
 
If any of us had any hard and fast rules we would have shared them already. 😁

It sounds like you’ve got the most trailer repair experience among the commenters, so you’re probably the one with the information needed to answer your question. You’ve told us the tolerances you currently use, but not the errors of the trailers as they come to you. The errors you’re being asked to fix should give you a clue to what errors are acceptable.

I have noticed that once a customer has noticed an error they become hyper-aware of it, so a repaired item usually has to meet a higher standard than a new item would.

Why do you want to mediate between the dealer and the customer?

In your shoes I’d never talk to anyone but the dealer, talking to customers is their entire job. Have you asked them or the trailer manufacturer about acceptable tolerances?


Oooh, I’m thinking about angles backwards! If the axle is square to the frame, then the trailer will track parallel to the tow vehicle offset by the error(length is irrelevant). If the axle Is out of square, it will shift sideways until the wheels are pointed in the direction of travel: longer trailer more displacement because the error originates at the axle, not the hitch like I was thinking about it.

I apologize for dragging the thread off topic. Dammit, I guess I have to thank Thermite for explaining it to me in his unique style.
 
fciron, I don't talk to the customer, however, I want to be fair to the customer at the same time, they spent a lot of money and should get a good product.

I totally agree, when I do fix them, I try to hold 1/16" because like you said, they are hyper sensitive about the issue.

Thanks for your time and comments.
 
I have built a handful of trailers. I have also sectioned, reassembled and repaired a lot of vehicle frames from pickups through class 8 trucks. I understand the problem.

However, I fail to see how the coupler being off center by a fraction of an inch makes a damn bit of difference.

I have a hitch ball welded onto one corner of the blade on my excavator. You know what happens when I pull a trailer with it? The trailer pulls straight, but offset half the blade width. (duh) Same would happen if the coupler was offset by some amount.

If the coupler is reasonably close, the only thing you should give a shit about is that the axles are aligned to the centerline of the trailer. If they are, trailer will pull straight.

To line up big stuff I have built and modified including trailers I use plumb bobs to the floor. I like to set pieces of flatbar on the ground instead of chalk lines so I can measure a little easier.

For real tricky measurements I have even used a little Bosch laser tape measure thing. I was hesitant, but it worked well. I use the same tool to line up all my machines in my shop so they are square with the building.
 
Qt: (I use the same tool ( Bosch laser tape measure thing) to line up all my machines in my shop so they are square with the building.

Good. you would not somebody looking out the not perfectly squared off window and so missing the exit door and then slamming nose-first into the brick wall.

Osha would be all over that.."Why did you put this door here"
 
I have built a handful of trailers. I have also sectioned, reassembled and repaired a lot of vehicle frames from pickups through class 8 trucks. I understand the problem.

However, I fail to see how the coupler being off center by a fraction of an inch makes a damn bit of difference.

I have a hitch ball welded onto one corner of the blade on my excavator. You know what happens when I pull a trailer with it? The trailer pulls straight, but offset half the blade width. (duh) Same would happen if the coupler was offset by some amount.

If the coupler is reasonably close, the only thing you should give a shit about is that the axles are aligned to the centerline of the trailer. If they are, trailer will pull straight.

To line up big stuff I have built and modified including trailers I use plumb bobs to the floor. I like to set pieces of flatbar on the ground instead of chalk lines so I can measure a little easier.

For real tricky measurements I have even used a little Bosch laser tape measure thing. I was hesitant, but it worked well. I use the same tool to line up all my machines in my shop so they are square with the building.
I guess it depends what you call some !
 
well they really should be damn near perfect from the manufacturer
you know stacking of slight out of whack can become big deal.

now the one you aren’t getting to check is the tow setup the customer has
 
The catch with all the exact dimension theories is the springs....triler springs have a consider camber ,and load the spring the camber flattens,moving the wheel back .....this is often called self steering ,and can cause the wild sway you sometimes see (sway is also caused by weakness in the towing vehicle).......track rods /radius rods is one cure,but a much cheaper one is very high load springs .....shorter and thicker/more leaves deflect minimally at high load..
 
However, I fail to see how the coupler being off center by a fraction of an inch makes a damn bit of difference.
^^^^ this

The hitch being off a bit doesn't have anything to do with a trailer pulling down the road at an angle. (Actually, the worst part about a trailer like that is trying to back it in a straight line!) The only thing that affects it pulling down the road is the axle position. You could have a trailer shaped like an S and it's still going to go down the road with the axle pointed straight ahead. Fix the hangers and stop wasting time on the coupler!
 
I have a hitch ball welded onto one corner of the blade on my excavator. You know what happens when I pull a trailer with it? The trailer pulls straight, but offset half the blade width. (duh) Same would happen if the coupler was offset by some amount.

If the coupler is reasonably close, the only thing you should give a shit about is that the axles are aligned to the centerline of the trailer. If they are, trailer will pull straight.
I have built a handful of trailers. I have also sectioned, reassembled and repaired a lot of vehicle frames from pickups through class 8 trucks. I understand the problem.

However, I fail to see how the coupler being off center by a fraction of an inch makes a damn bit of difference.

I have a hitch ball welded onto one corner of the blade on my excavator. You know what happens when I pull a trailer with it? The trailer pulls straight, but offset half the blade width. (duh) Same would happen if the coupler was offset by some amount.

If the coupler is reasonably close, the only thing you should give a shit about is that the axles are aligned to the centerline of the trailer. If they are, trailer will pull straight.

To line What?
I have built a handful of trailers. I have also sectioned, reassembled and repaired a lot of vehicle frames from pickups through class 8 trucks. I understand the problem.

However, I fail to see how the coupler being off center by a fraction of an inch makes a damn bit of difference.

I have a hitch ball welded onto one corner of the blade on my excavator. You know what happens when I pull a trailer with it? The trailer pulls straight, but offset half the blade width. (duh) Same would happen if the coupler was offset by some amount.

If the coupler is reasonably close, the only thing you should give a shit about is that the axles are aligned to the centerline of the trailer. If they are, trailer will pull straight.

To line up big stuff I have built and modified including trailers I use plumb bobs to the floor. I like to set pieces of flatbar on the ground instead of chalk lines so I can measure a little easier.

For real tricky measurements I have even used a little Bosch laser tape measure thing. I was hesitant, but it worked well. I use the same tool to line up all my machines in my shop so they are square with the building.
What???

In these dynamics there is no “trailer”
The frame and all thoughts of being square to its components are irrelevant.

Take an axle set, draw a circle of r= the distance of that axle to the ball.
Draw a line from ball center to the axle center.
Square the axle to that line.

An exercise of moving the hitch across the blade of a tow vehicle is irrelevant to that geometry.

Now since we are sane people…
If one has a rectangular shaped trailer and we want to proceed down the road with the box parallel to direction of travel, insure that the above ball/axle geometry has its axial alignment corresponding with the trailer box.
 
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The reason the OP is so concerned about coupler location, is he's determining axle alignment off the coupler, not off the frame. A basic triangle measurement from coupler down to the spring hanger on each side. Which, if the coupler is out of center, using that triangle measurement to square the axles will result in a frame that crabs off center. The wheels were true to the coupler, so the three points of contact (wheels to ground, and coupler to tow vehicle), are running true, but the box or bed aren't on the same wavelength.

My question is if that's the right approach, or should the OP be squaring up axles in a different manner, to avoid charging a customer to fix a problem that's otherwise immaterial. From a driver noticeability standpoint, if the axles are square with the part they can see in the mirror (the frame, the box, etc), the trailer will appear to be true even with quite a lot of coupler offset (maybe even an inch). As long as the frame is traveling precisely parallel with the road lane, who cares if it is ever so slightly out of center?

Instead of cutting tongues off all these trailers, should he instead be simply squaring the axles to the frame, and ignoring the coupler unless it's egregiously off (say 3/4" or more)? I'm thinking it may make more sense to be pulling the spring hanger triangulation measurement off the center of the box, deck, first major crossbar of the frame, etc, and only worry about crazy couplers.

I'm assuming centering the coupler is usually involving cutting off the entire tongue triangle, so a lot of labor for very little gain if axle alignment can be figured in a different manner.
 
The reason the OP is so concerned about coupler location, is he's determining axle alignment off the coupler, not off the frame. A basic triangle measurement from coupler down to the spring hanger on each side. Which, if the coupler is out of center, using that triangle measurement to square the axles will result in a frame that crabs off center. The wheels were true to the coupler, so the three points of contact (wheels to ground, and coupler to tow vehicle), are running true, but the box or bed aren't on the same wavelength.

My question is if that's the right approach, or should the OP be squaring up axles in a different manner, to avoid charging a customer to fix a problem that's otherwise immaterial. From a driver noticeability standpoint, if the axles are square with the part they can see in the mirror (the frame, the box, etc), the trailer will appear to be true even with quite a lot of coupler offset (maybe even an inch). As long as the frame is traveling precisely parallel with the road lane, who cares if it is ever so slightly out of center?

Instead of cutting tongues off all these trailers, should he instead be simply squaring the axles to the frame, and ignoring the coupler unless it's egregiously off (say 3/4" or more)? I'm thinking it may make more sense to be pulling the spring hanger triangulation measurement off the center of the box, deck, first major crossbar of the frame, etc, and only worry about crazy couplers.

I'm assuming centering the coupler is usually involving cutting off the entire tongue triangle, so a lot of labor for very little gain if axle alignment can be figured in a different manner.

This is exactly how I see it as well. I square axles to the centerline of the trailer. No fucks are given to the location of the coupler in relation to the axles.

I can't think for the life of me why anyone would think it was a good idea to mount the axles using a radius from the center of the coupler.
 
What???

In these dynamics there is no “trailer”
The frame and all thoughts of being square to its components are irrelevant.

Take an axle set, draw a circle of r= the distance of that axle to the ball.
Draw a line from ball center to the axle center.
Square the axle to that line.

An exercise of moving the hitch across the blade of a tow vehicle is irrelevant to that geometry.

Now since we are sane people…
If one has a rectangular shaped trailer and we want to proceed down the road with the box parallel to direction of travel, insure that the above ball/axle geometry has its axial alignment corresponding with the trailer box.

I think you missed the point and are not visualizing any of this well?

Key points-

1- side-side offset of coupler has dick to do with offset of trailer in the lane past the actual (meaningless) offset of the coupler as it relates to the centerline of the trailer.

2- The axles are squared to the trailer's frame or it's "center of mass". There's no imaginary radius from the ball coupler. That's just dumb. It adds a whole nuther level of error into the problem. Axles square to frame; trailer's travel direction will align with it's centerline.
 








 
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